Re: I too am going to montana and jackson hole.
snowpack in the area is around 100% right now, so most waters will be running high and murky. however, thanks to thermal activity by the headwaters, the firehole in yellowstone is at its peak during late spring/early summer. it can be a challenging river, but there are plenty of nice trout. generic nymph patterns and BWO's should work well, along with some of the best evening caddis hatches i've ever fished. i had great success last june with Craig Mathews' iris caddis, check him out at blueribbonflies.com . good luck!